Great improvements achieved in recent years in the properties of catalysts for polymerizing olefins have remarkably increased the polymer yield per unit amount of the catalyst used, consequently reducing the amount of transition metal catalyst remaining in the polymer produced and eliminating the need for the step of removing the catalyst.
While the processes for polymerizing olefins include the slurry polymerization process, bulk polymerization process, gas phase polymerization process and the like, elimination of the catalyst removing step has directed attention to the gas phase polymerization process in which recovery of the solvent and the purification step can be dispensed with and which readily permits recovery of the monomer and drying of the polymer product.
To smoothly effect such gas phase polymerization, generally used are fluidized bed reactors or this type of reactors having an agitator, in which an olefin or olefin-containing gas is subjected to polymerization while fluidizing solid particles including olefin polymer particles and catalyst particles in suspension in a fluidized bed forming region within the reactor. The reactor is operated by continuously supplying the material, catalyst and polymerization gas and continuously discharging the polymer product.
FIG. 1 shows a typical example of gas phase polymerization apparatus having an agitator in a fluidized bed polymerization reactor. The apparatus comprises a polymerization reactor 1, gas distributor 2 incorporated into the reactor, gas room 3 separated off by the distributor 2 and positioned thereunder, fluidized bed 4 formed by a catalyst and a polymer product above the distributor 2, polymerization catalyst supply channel 5, polymer product discharging channel 6, circulation gas inlet 7 communicating with the gas room, circulation gas outlet 8 communicating with the fluidized bed forming region, replenishing material feed channel 9 and circulation gas compressor 10. The agitator used is a usual agitating device having anchor blades, turbine blades, flat plate blades or like blades (not shown).
Unexamined Japanese Patent Publication SHO 58-154702 discloses use of a gas distributor in the gas phase polymerization reactor of the type described for polymerizing olefins which distributor has holes and caps covering the respective holes from above and each having an opening in one direction in order to prevent the distributor from clogging and prevent particles of polymer product from falling into the gas room.
However, the above gas distributor encounters a problem if it is attempted to increase the polymerization capacity of the reactor because in the region above the distributor and thus the region in the discharging channel 6, the gas solid ratio (gas (kg) per unit volume/solid (kg) per unit volume) increases, that is, the amount of gas to be discharged from the fluidized bed increases to result in a reduced efficiency in discharging the polymer product from the fluidized bed.